1. Field of the Invention
The present invention relates broadly to the field of electronic musical instruments, electronic tone generators, and electronic musical controllers. In particular, the present invention relates to a method and apparatus for controlling expressive musical articulation by controlling the duration, overlap, and timbre assignment of successive tones as a function of playing speed.
2. Description of the Related Art
Electronic musical instruments comprise two distinct systems: a tone generator and a controlling interface (controller). The two systems can be embodied in a single device or as two entities that are interconnected. A controller transduces the physical gestures of the performer and sends performance data to one or many tone generators. At a minimum, the performance data includes a pitch and a note-on signal, with optional additional data representing other musical parameters such as velocity. Some controllers sense and transmit note-off data. Typical controllers are a piano-like keyboard, an array of drum pads, or a keyed wind instrument. Another type of controller is a sequencer, which is a program that stores performance data (either recorded from another controller or entered by hand) and replays the data automatically. Further, a controller can be a computer that computes performance data and transmits the performance data over a data transmission line (e.g., a dedicated data transmission line, a data transmission line within a network system, or the Internet) to a tone generator.
Traditionally, a performer controls articulation by varying musical attributes relating to the perceived "connectedness" of a sequence of notes. There are two main ways to control this effect. One method is to control the time when notes begin and end, thereby controlling the duration of each note and the degree of overlap or detachment among successive notes. Another method is to vary the shape of the amplitude envelope of a note, particularly the speed of the attack (ramp-up in volume from silence or the previous note upon a new note-on action) and release (ramp-down to silence upon note-off action).
One attribute of articulation is the degree of overlap between successive tones. A continuum ranging between "legato" and "staccato" can be used to characterize the articulation of tones. Legato is characterized by slow attack and perceivable overlap between successive tones. Staccato is characterized by fast attack and an interval of silence between tones.
The ability of a performer to control legato/staccato depends on the particular capabilities of the tone generator and controller combination employed. In particular, the degree of legato overlap effect cannot be controlled unless the player can manipulate the controller so as to send separate note-on and note-off signals to the tone generator and the tone generator has the ability to sustain a tone indefinitely and to produce many tones simultaneously.
Continuous controllers, like piano or organ keyboards transmit note-on messages on key depress and note-off on key release. This permits great flexibility in articulation, but can also work to the disadvantage of some players, who may have difficulty performing fast passages where notes "smear" because the keys are not released quickly enough.
Percussive controllers, such as drum pads/triggers or marimba-like arrays of pads respond only to the initial stroke and note duration is controlled indirectly by automatically sending a note-off after some time interval has elapsed. The interval is either fixed or velocity-sensitive (i.e., the duration of the note is a function of the speed at which the drumstick strikes the pad), and is determined at the time of initial gesture and unchangeable thereafter. Fast musical passages can result in blurred sound where many notes of fixed duration overlap.
In current practice, it is common to achieve a legato effect by controlling the attack and decay rates of the amplitude envelope, or by connecting notes in a monophonic fashion, allowing only one tone to sound at a time.
Many continuous and percussive controllers can measure the velocity of the initiating note-on gesture (speed of key-down or mallet stroke, puff of air) and the tone generator can use this data to control rate of attack. Some keyboard controllers can sense the speed of note release and use this information to control release rate. In both cases, the effect is determined at the time of the initiating gesture and applies only to the note associated with that gesture.
The duration of a tone depends on the player's ability to control the moment of note-off (i.e., when the release segment of the envelope begins) and is limited by the affordance of the particular controller being used. In particular, keyboard-like controllers send a note-off signal upon key release, and percussive controllers predetermine note duration at the time of note-on.
Current practice either imposes no constraints on the number of notes with legato envelopes that can sound simultaneously or limits legato to strictly monophonic mode where one tone sounds at a time. When a legato passage is played it is useful to allow only two notes to be sounding at the same time in order to have some amount of overlap while avoiding a blurred effect. The amount of overlap should be adjusted to account for the speed of consecutive notes in a musical passage.
When an electronic instrument allows variable articulative control over envelope and duration, it is always on a note-by-note basis. This can be a problem when a group of notes is performed together in a chord. Individual notes may have different envelopes resulting in an unpleasant balance, or the duration of notes may differ so that the chord is released in a ragged way, each note at a different time.
The Studio Vision sequencer program from Opcode has a legato mode operation that can be applied to a selected range of notes in a sequence. This program will change the duration of each selected note so that it extends a given percentage of the way to the next note. This feature is an editing operation that must be applied to a recorded sequence out of real time; it cannot be used while actually playing.
The Kurzweil K2500 tone generator has a "Legato Play" mode. In this mode a note will play the attack segment of its amplitude envelope only when all other notes have been released. The K2500 also has a legato switch which causes the instrument to behave in a monophonic fashion: whenever a new note is begun, the previously sounding note is immediately terminated.
The "malletKAT" is a MIDI (musical instrument digital interface) controller that resembles a xylophone. It has a mono mode overlap feature which provides a fixed overlap interval between successive notes; when a new note is started the previous note is terminated after the fixed interval has elapsed. The overlap interval does not change and the feature is available only when the controller is in monophonic mode; thus, chordal or polyphonic performance of many simultaneous tones is impossible.
U.S. Pat. No. 5,142,960 describes a keyboard instrument that produces a legato-type envelope depending on a predetermined playing style and instrument timbre. The legato effect is strictly monophonic; it is produced when a new note-on is received and another note its still sounding. The release of the old note and attack of the new note are forced to be coincident and shaped by a predetermined amplitude envelope with relatively small attack for the new note. No overlapping of the two notes occurs.
U.S. Pat. No. 4,332,183 describes a keyboard instrument which distinguishes between two states, legato and non-legato, depending on the speed of successive key-down signals, and applies legato or non-legato ADSR envelopes on a note-by-note basis. The duration of notes is not controlled, the overlapping of successive legato notes is not controlled, and the number of simultaneously sounding legato notes is not constrained. All non-legato notes are treated the same, whether they are part of a chord or a polyphonic passage.
U.S. Pat. No. 4,424,731 describes a device for selecting one of two fixed durations for percussive tones such that when many keys are played in quick succession the duration is set shorter to avoid excessive overlap. This device concerns percussive tones with fixed durations and which are incapable of being sustained indefinitely.
U.S. Pat. No. 5,365,019 describes a touch controller that adjusts the note-on velocities according to playing speed. The time interval from the immediately preceding note-off or note-on is used to adjust the touch velocity so that the degree of responsiveness to force of touch varies with playing speed. The disclosed device includes means for altering the touch effects of a new note when a note-on is received. It does not control the duration of a tone or affect any attributes of previous notes.
Changing the attack and release rates of amplitude envelopes modifies the timbre of a note slightly, but the tone is still recognized as a variant of the same instrument. Some electronic musical instruments provide mechanisms for selecting and mixing multiple instrumental timbres for each note or a range of notes.
One such feature is known as "keyboard split", whereby a predetermined contiguous range of pitches is played in a particular timbre while another disjunct range is played in a different timbre (e.g., C2-B3 bass, C4-C6 piano). The ranges and timbre assignments are preset and cannot be changed during performance.
Another timbre selection method is "velocity mapping", whereby a pair of timbres is assigned to a range of pitches. A mix of the two timbres is controlled by the force of the player's note-on actions, (e.g., at soft levels 100% timbre A and 0% timbre B, at medium levels 50/50 mixture of the two timbres, at loud levels 0% timbre A and 100% timbre B). This sort of timbre selection is subtle and difficult to control, since it is hard to reliably reproduce the same force on repeated key strokes.